i had the same prob with my M47 (a mechanic said he cant weld onto a plug),the good news is that once i got it off i used new plugs and washers and it now leaks..the joy

I had to replace the clutch and while the gearbox was out the mechanic Tig welded a nut to the level plug which was the hardest one to remove. It was then
possible to remove it. Thanks to all for your input.
Regards Bruin

I solved this problem on the filler bolt by spraying with pentrating oil (Gunk), then tapping on the bolt with a hammer for a few minutes to encourage the oil to get in a bit more. I did this for 3 nights in a row. On the next night, I used a pipe wrench (because I had already rounded the bolt by that point) and it came off very easily.

Had the same problem w/ mine. Just couldn't get the fill plug out and chewed it up completely. My son had a good idea and he welded a 17 mm bolt to the plug. Is was really amazing though because after all that straining and cus'n to get the plug out it practically came out by hand after the bolt was welded on!!! The heat from the welding must have done the trick.

I had the same problem because a PO had really tightened the top plug instead of using a gasket. Ground down the flats to try to get a grip until there was almost nothing left, then left it for a while. Checked it a couple weeks later and saw oil weeping from it -- ATF is supposed to be a good penetrating oil, its just slow. At that point I was able to turn it out with a cold chisel. Already had purchased new pluds at that point.